9) $$4x^2-7x^4 - (2x^2 - 4x^4-x^3) + (-x^3+x^4) = 4x^2 - 7x^4 - 2x^2 + 4x^4 + x^3 - x^3 + x^4 = -2x^4 + 2x^2$$
Ответ: $$-2x^4 + 2x^2$$